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STEENS MOUNTAIN

In southeast Oregon

You may have heard of "the Steens mountains" in Oregon. They don't exist. There is only one mountain there: Steens Mountain.

Steens is a fairly large block of mostly lava about 50 miles long, one edge of which was uplifted as a single block. The east face, what we see here, is the dramatic side of the mountain as it rises about 5,000 feet above the desert floor next to it. The west side is a rather unremarkable gentle but relentless upslope.

Geologists say that it is made of two basic blocks of lava, each consisting of a number of individual flows. Both are called "flood basalts," meaning that the lava was fairly liquid and flowed freely.

The lower, earlier flow is believed to have originated from the Yellowstone Hotspot when it was just to the south (off the left edge of the photo) of this mountain. The upper block also came from the Yellowstone hotspot when it was farther away, but not yet in its present location, and is part of the Columbia River Basalt Group.

These flows happened mostly from 17 to 14 million years ago. The uplift happened 9 million years ago. Geologists disagree about what caused the uplift.

That's about all I know at this juncture, and I probably have part of the story wrong.
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THE SAN RAFAEL REEF
At the edge of The Swell

This reef marks the eastern edge of the San Rafael Swell, which is a relatively small block of about 900 square miles that was forced eastward & upward over older formations during the Laramide Orogeny (see my other posts for info about the Laramide). This is the view from Interstate 70 as you ascend (westbound) or descend (eastbound) to/from the top.

The top, as can be expected, is relatively flat with steep canyons carved into the Navajo sandstone (the primary formation you see in these flatirons), which is far more erosion-resistant than the layers above or below it. Here at the fault, the Navajo Formation (which is a few hundred feet below the ground at the camera's location) has been tilted upward by the ground behind it.

It is worth spending a day on top (spring & fall only!) crossing the Swell in both directions and stopping at all of the scenic vistas. The canyons behind this wall have hidden rustled cattle and horses stolen by some of the most famous outlaws of the Old West, including Butch Cassidy himself. You won't need four wheel drive, but DO bring at least a liter of water per person, even in the springtime. If you do this in the summer, increase the ration to a gallon.

Geotagged if you want to go here. Click on the picture, click on the three dots at the upper right corner of your browser, and choose "Show Information."
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THE BOOK CLIFFS

Named by Capt. John Gunnison in 1853 when one of his men mentioned that they looked like "books on a shelf." They run hundreds of miles from Price, Utah to Grand Junction, Colorado.

This is Mancos Shale (the furrowed grey stuff) overlain by formations in the Mesa Verde group. As I mentioned a couple of days ago, the Mancos was mud deposited in an interior seaway about 95-80 million years ago, and the Mesa Verde formations were deposited as the seaway retreated northward.

The Mancos is very soft and erodes easily, so it is normally only seen underneath the harder Mesa Verde, which protects it. Or where there is so much of it that it hasn't all washed away yet, as seen in the lower left corner of the photo.

This is just north of the town of Green River, Utah. The Green is the river at the bottom of the photo.
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THE LA SAL MOUNTAINS
of Eastern Utah

I have been trying to get a decent shot of these mountains since I first laid eyes on them eight years ago. Today, after a very harrowing day, I happened to be driving by at exactly the right moment.

The La Sals are laccoliths: mountains made of lava that formed underground. The lava pushed up against the layers above them, fracturing them, but never broke through. After the lava cooled and solidified, the fractured layers of older rock above them were easily eroded away.

These mountains formed 30 to 20 million years ago. The red rock at the left edge of the picture is the 180-to-140-million-year-old Entrada Formation, with several older formations below it. You can still see the edge of the bulge where it was forced up by the laccoliths behind it.

The sharp-eyed viewer who has been to these parts will recognize the tips of the Fisher Towers just to the left of the center of the picture.

This is all near the outdoor recreation mecca of Moab, Utah.

#Utah #geology #laccolith
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GUNNISON BUTTE
and the Green River
Near Green River, Utah

Here at the mouth of Gray Canyon, the Green River has been cutting through the Tavaputs Plateau and the lower plateaus below it for 120 miles.

This rock is of the Mesa Verde group, underlain by what looks to me (I wasn't able to find an authoritative source) like Mancos Shale. Both were laid down in the late Cretaceous; the Mancos from about 95-80 million years ago, and the Mesa Verde immediately after that.

At that time there was a large interior seaway reaching southward into this area. The Mancos is mud that settled on the bottom of it, and the Mesa Verde formed as the sea started receding (source: Roadside Geology of Utah ). This is the last remnant of Mesa Verde rock at the mouth of the canyon.

Geotagged if you want to go here. The road is paved except for the last half mile; you can do it in an ordinary car.
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This is Square Butte on the Navajo Nation, near Page, Arizona.

I've been unable to find an authority telling me what we're looking at here, except one that says it's all Jurassic.

The purplish windswept sandstone at the bottom can only be Navajo Sandstone. Therefore, the red and white layers above it are, no doubt, Entrada sandstone.

NO idea what the stuff is on top. If anyone knows, please comment below.

#Arizona #geology #NavajoNation
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+Amrullah Hidayat asked in a comment in another post for something about "crystal systems."

This is all I have: a clump of selenium crystals in Capitol Reef National Park called "Glass Mountain" (which is not a mountain and isn't made of glass).

In the background are the features of Entrada sandstone (left behind when Cathedral Valley eroded away) known as Temple of the Sun (near) and Temple of the Moon (far).

Not sure how the crystals got formed. I don't know much about selenium.
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2/24/18
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Rabbit Valley, Colorado
View from my campsite.

Not sure if I should post this in my Geology collection, 'coz it's really more of a "brag photo - where I am" shot.

Rabbit Valley is two miles into Colorado from the Utah state line. I'm camped up on its rim with this nice view.

The gray stuff near the photo center is a dinosaur-bone quarry in Morrison Formation mudstone. It is open to the public, and there's a "Trail Through Time" hike you can take that features a stegosaurus spine still embedded in the rock!

This point is at the very end of the Uncompahgre Uplift, and we are looking south-eastward along its backbone. In the distance can be seen the pinkish Entrada Formation sandstone, which is well below the Morrison Formation, that has been uplifted and exposed by erosion.

It's very quiet up here. I like it.
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The Roan Cliffs
In the Piceance Basin of Western Colorado / Eastern Utah

Above and behind the 200-mile-long Book Cliffs that stretch from Price, Utah to Grand Junction, Colorado is another set of higher cliffs that cannot be seen from the highways in the valley below. They are the Roan Cliffs, and you have to get up on top of the Book Cliffs to see them.

The whitish material at the top is the Green River Formation; the variously-colored reddish material below it is the Wasatch Formation. Both were deposited in a huge inland basin some 50 million or so years ago, after the dinosaurs died out.

Both formations are a significant source of coal, oil and gas. Indeed, I was standing at a gas well when I took this photo.

The Piceance Basin is a desolate place. Hardly anything grows here and there isn't much of anything here to interest anyone except for oil company geologists.

This is in Coal Canyon immediately north of Fruita / Grand Junction, Colorado.

Added later: Piceance is pronounced "Pee-awnse"

#Colorado #geology
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The Fort Steele Breaks
Near Sinclair, Wyoming

North of Sinclair, Wyoming is a small anticline called the "Fort Steele Anticline." It is made of rock from the Mesa Verde group of formations.

At this point, the North Platte River has cut its way through the anticline, revealing a series of hogbacks left after overlying rock has eroded away.

The sharp-eyed viewer can see, in the cut through the nearest hogback on the left side of the photo, that the layers here slope away from the camera -- meaning that the middle of the anticline is somewhere behind us.

Not very scenic here; I post this mainly because hogbacks just fascinate me --and we have four of them together here.

#wyoming #geology
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